The present invention relates to an apparatus for preventing collision of a vehicle which imparts a damping of a driving vehicle according to a preset deceleration without being affected by a condition of contact between a surface of road or railway and wheels of the vehicle.
Heretofore, it has been known to provide an apparatus for preventing collision of a vehicle by damping the vehicle by measuring a distance R from the driving vehicle to an obstacle such as a forward vehicle or a stopping vehicle and a relative velocity V thereof and damping the driving vehicle by generating a damping signal when the relation of EQU R-R.sub.0 &lt; (V.sup.2 /2.alpha.)
wherein R.sub.0 represents the nearest distance and .alpha. represents a preset deceleration, is given.
The damping apparatus has been employed for preventing the collision of vehicles. Referring to FIG. 1, the known damping apparatus will be illustrated in detail.
In FIG. 1, the distance R from the vehicle to the obstacle is plotted on the abscissa and the relative velocity V is plotted on the ordinate.
The driving vehicle approaching to the obstacle at a relative velocity of V = V.sub.1 = constant can be shown as the line 11. When the curve 12 is shown by R-R.sub.0 = V.sup.2 /2.alpha., the curve 12 crosses the line 11 at the distance of R.sub.1 - R.sub.0 = V.sub.1.sup.2 /2.alpha.. The cross point is given as A. The driving vehicle approaching at a constant velocity V.sub.1 is controlled with a constant damping by the damping signal for the preset deceleration .alpha. at the cross point A.
Thus, if the actual deceleration .alpha.' of the vehicle has resulted because of the effect of friction between the wheels (tires) and a surface of road, the vehicle gradually approaches the shortest distance R.sub.0 to the obstacle along the deceleration curve 12 in the case of .alpha. = .alpha.', whereby the relative velocity of the driving vehicle becomes zero in the shortest distance R.sub.0 and the driving vehicle avoids collision with the obstacle.
Thus, even though the damping is generated by the preset deceleration .alpha., it is rare that .alpha. precisely equals .alpha.' because of the effect of friction between the surface of road and the wheels.
One way to overcome this problem is to determine the deceleration .alpha. after considering the effect of the friction between the surface of the road and the wheels. However, the effect of friction are not easily determined because of the number of variables involved.
In the case of .alpha.' &gt; .alpha., excess damping is applied and the curve 13 from the point A in FIG. 1, and the relation of R - R.sub.0 &gt; V.sup.2 /2.alpha. is given at a certain point on the curve 13 to release the damping signal whereby the driving vehicle drives at a constant velocity toward the point C on the curve 12.
Thus, the damping is also applied at the point C and the excess damping phenomenon is repeated at the points D and E. The intermittent dampings are applied and a smooth damping can not be attained.
The intermittent damping is applied because of the delay of the mechanical system of the damping apparatus from the time of the generation of the damping signal to the actual performance of the damping operation.
In the case of .alpha.' &lt; .alpha., the driving vehicle has the velocity V.sub.2 even in the nearest distance R.sub.0 as shown by the curve 14 in FIG. 1. Therefore, when .alpha.' &lt; .alpha. there is a possibility of a rear-end collision with the forward obstacle (vehicle, etc.) which is quite a dangerous condition.